This invention relates to a pigment composition for a high build protective coating such as paint.
Heretofore in the art to which my invention relates, pigment particle size has been limited by the practice considerations of pigment settling during the storage of liquid paint, and of protrusion of particles from thin paint films and the tendency of large particles to stop up spray application equipment. Commercial fillers designed for coatings seldom contain more than a very small fraction of particles which fail to pass a 325 mesh (44 micron) sieve. Because of these limitations protective coatings formulators have not taken full advantage of the phenomenon of particle packing, which is utilized by other workers in such diverse fields as selection of concrete aggregate and formulation of calking compounds. Efficient particle packing permits the formation of dense compositions which contain high volumes of aggregate or filler but which nevertheless have excellent physical properties. However, in order for particles to pack efficiently the particle size range must cover two orders of magnitude with substantial numbers of particles near both ends of the range. In order to meet this criterion using conventional paint pigments with their limited maximum diameters, formulators must employ major quantities of pigments having small particles of less than 0.5 micron diameter. The use of such fine particles increases the total particle surface area which retards flow, increases viscosity which reduces the non-volatile materials whereby more expensive materials are required and at the same time dispersion of the pigments is more difficult. Such small particle size pigments also lead to very short inter-particle distances which cause rapid failure of corrosion protection by film break-down during water immersion.
Definitions of the word "pigment", as used in the paint industry are set forth in the following publications: Webster's New International Dictionary, Second Edition, page 1860; Principles of Color Technology by Billmeyer and Saltzman, page 93 (Interscience, New York 1966); Federation Series on Coatings Technology, Unit 7, White Hiding and Extender Pigments, page 7 (Federation of Societies for Coatings Technology, Philadelphia, Pennsylvania, 1967); Paoint Technology Manuals, part 6, Pigments, Dyestuffs and Lakes (OCCA publication); Reinhold, New York, 1966); and, Pigment Handbook by Temple C. Patton, Volume 1, Page VII (John Wiley and Sons, New York, 1973).